Solar energy from space gets closer by launching satellite
By: Kas Schonebeek
A satellite with test instruments to generate solar energy in space was launched last week. Researchers at Caltech are trying to tackle a number of very complex problems with this.
Roofs, meadows and deserts are becoming increasingly full of solar panels. At the same time, there is a growing awareness that the surface of the earth is not infinite and that the sun does not provide a constant supply of energy - clouds, changing seasons and the night play tricks on sunshine.
That is why people are looking up: would it be possible to generate solar energy in space, where the sun always shines? A satellite was launched this week that is researching several crucial aspects to make solar energy from space a success.
Caltech, one of the world's leading technical universities, has been working for ten years on the Space Solar Power Project (SSPP), which is to collect solar energy 500 kilometers above the earth and send it to earth. The promise is great: the yield of a solar cell outside the atmosphere is in theory eight times higher than on Earth. The research group was funded with $100 million by philanthropist Donald Bren, who became fascinated with the subject in 2011 when he read an article in Popular Science magazine. What sounded like a science-fiction fantasy at the time is now being tested.
Three major challenges
A SpaceX rocket blasted a Caltech prototype, the Space Solar Power Demonstrator (SSPD), into space on Tuesday. Three instruments are mounted on a probe, each of which examines one of the solar energy bottlenecks in space.
The first obstacle is the solar cells themselves. To make energy from space profitable, large amounts of electricity must be generated. A commercially viable system will consist of at least a few square kilometers of solar cells. Modern solar panels that are now used in satellites are also too cumbersome and too heavy to be transported to space in huge numbers. The researchers have therefore developed solar cells that have a yield per kilo weight fifty to one hundred times higher than existing space solar cells. The SSPD tests 32 different designs to see which works best in practice.
The second problem also has to do with the solar cells. Because how do you ensure that you get a gigantic field of solar cells in an elongated rocket? The answer: fold them smartly. Like the recently launched James Webb telescope, the solar cells are folded and unfolded in an origami-like manner. But where the sunshade of the James Webb is 'only' about twenty by twenty meters in size, the SSPP must consist of hundreds of tiles, each up to 60 meters long. The prototype now has a modest size and works with tiles of about 10 square centimeters.
But these problems pale in comparison to the final bottleneck: getting the generated energy back to Earth. The solar energy must be sent wirelessly to the earth over hundreds of kilometers. A super-lightweight system has been developed for this purpose that converts the energy into radio waves - a form of electromagnetic radiation. All solar cells individually emit radio waves and are precisely tuned to each other. This creates one focused beam of radio waves with a very high power. That beam must be collected again on Earth. For the time being, the test system does not go much further than half a meter. A working solution to bridge the gigantic distance to Earth is still a long way off.
Caltech isn't the only one working on solar energy from space. The Chinese Xidian University has built a test setup on the ground that has succeeded in transmitting energy over a distance of 55 meters using radio waves. The Chinese researchers expect that it will take several generations before the technology for generating solar energy in space can be used.
Closer to home, the European Space Agency ESA is taking the first baby steps towards generating energy in space. It is being investigated whether it is feasible to set up a research line comparable to SSPP. The ESA has until 2025 to make a decision on this.
The work being done by researchers is really inspiring.